Switching from rituximab originator to GP2013 or CT-P10 biosimilars in autoimmune rheumatic diseases: drug retention rate and safety data from a multicentric retrospective cohort

Background: Real-world evidence supporting a safe and effective transition from rituximab originator (RTX-O) to its biosimilars (RTX-B) in autoimmune rheumatic diseases (ARDs) is still limited. Objectives: The primary aims of this study were to evaluate the long-term persistence of RTX-B after the non-medical switch (NMS) from RTX-O in ARD patients, and to explore the RTX-B safety profile. The secondary aims were to evaluate the impact of different factors on RTX-B drug retention rate (DRR) and to identify any factors associated with RTX-B discontinuation. Design: Retrospective observational study. Methods: We included consecutive ARD patients undergoing NMS from RTX-O to GP2013 or CT-P10 from January 2018 to December 2020. RTX-B DRR was estimated by Kaplan–Meier plot analysis and compared according to different factors by the Log-rank test; the Cox proportional hazard model was used to detect factors associated with RTX-B discontinuation in the first 36 months. Results: We enrolled 181 patients switching to RTX-B: GP2013 in 143 (79.0%) cases and CT-P10 in 38 (21.0%). The estimated DRR for RTX-B was 81.5% at 12 months, 80.6% at 24 months, and 77.4% at 36 months. The incidence of adverse events with RTX-B was 12.6/100 patients/year. In the Log-rank test, no statistically significant differences were observed in the RTX-B DRR according to sex (p = 0.171), ARD diagnosis (p = 0.281), and concomitant immunosuppressive therapy (p = 0.054); on the contrary, patients on GP2013 showed a higher DRR than those on CT-P10 (p < 0.001). In the Cox proportional hazard analysis, the switch to CT-P10 was associated with a higher probability of stopping treatment (hazard ratio, 1.83 (confidence interval, 1.10–3.04), p = 0.02). Conclusion: NMS to RTX-B is associated with a high chance of retaining the drug for up to 36 months, irrespective of the diagnosis. GP2013 showed a higher retention rate than CT-P10.